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Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf
Marie-Béatrice Forel, Eugen Grădinaru
To cite this version:
Marie-Béatrice Forel, Eugen Grădinaru. Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf.
European Journal of Taxonomy, Consortium of European Natural History Museums, 2020, 727, pp.1 - 83. �10.5852/ejt.2020.727.1183�. �hal-03098408�
https://doi.org/10.5852/ejt.2020.727.1183 www.europeanjournaloftaxonomy.eu 2020 · Forel M.-B. & Grădinaru E.
This work is licensed under a Creative Commons Attribution License (CC BY 4.0).
M o n o g r a p h
urn:lsid:zoobank.org:pub:85AF63D9-5E9E-4CE0-AEC6-6F7CC8C4D375
Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen
into the Romanian Black Sea shelf
Marie-Béatrice FOREL
1,*& Eugen GRĂDINARU
2,*1 Muséum national d’histoire naturelle, CR2P, MNHN-CNRS-SU, 8 rue Buffon (CP38), 75005 Paris, France.
2 Department of Geology, Faculty of Geology and Geophysics, University of Bucharest, Bd. Bălcescu Nicolae 1, RO-010041 Bucharest, Romania.
* Co-corresponding authors: marie-beatrice.forel@mnhn.fr; eugen.gradinaru@g.unibuc.ro
1 urn:lsid:zoobank.org:author:063C1F7E-6D26-48F9-A8B1-2AFA496B5FB8
2 urn:lsid:zoobank.org:author:DE8A275A-486D-478F-9333-0FE0F7D30A78
Abstract. The present study evaluates the signifi cance of Triassic ostracods from the Romanian Black Sea shelf as part of a project for the understanding of the palaeoceanographical evolution of the offshore extension of the North Dobrogean Orogen. The drill core CM31, sampled from the borehole 817 Lebăda Vest drilled on the western Romanian portion of the Black Sea shelf, contains sediments of Rhaetian, Late Triassic age. The taxonomy of ostracods obtained is discussed and adds to the scientifi c understanding of marine ostracods during the Rhaetian stage. We document 72 species, of which seven are new: Histriabairdia pontuseuxinusensis Forel gen. et sp. nov., Bairdiacypris argonautaii Forel sp. nov., Ceratobairdia? akhilleusi Forel sp. nov., Isobythocypris atalantella Forel sp. nov., Petasobairdia amazonella Forel sp. nov., Paracypris ovidi Forel sp. nov. and Pseudomacrocypris? kerabani Forel sp. nov. Histriabairdia Forel gen. nov. is introduced to accommodate species of the Triassic–Jurassic interval previously attributed to the modern genus Anchistrocheles. These assemblages point to an outer shelf environmental with relatively normal marine oxygenation. The oldest occurrence of Pokornyopsis, found in this material, indicates that this forerunner of modern troglobitic ostracods may not have been troglobitic in the Triassic.
Keywords. Ostracods, Rhaetian, Late Triassic, Romanian Black Sea shelf.
Forel M.-B. & Grădinaru E. 2020. Rhaetian (Late Triassic) ostracods (Crustacea, Ostracoda) from the offshore prolongation of the North Dobrogean Orogen into the Romanian Black Sea shelf. European Journal of Taxonomy 727: 1–83. https://doi.org/10.5852/ejt.2020.727.1183
Introduction
Ostracods are millimetre-size crustaceans that are signifi cant components of the meiofauna. Recent ostracods live in various aquatic environments, from temporary freshwater ponds to hydrothermal
sources or cold methane seep sites (e.g., Horne et al. 2002; Maddocks 2005; Yasuhara et al. 2018), the deepest known living species occurring at a depth of 9307 m in the northwestern Pacifi c (Brandão et al. 2019). Some ostracods are commensal on diverse invertebrates or sea turtles (e.g., de Vos 1953;
Maddocks 1968; Tanaka & Hayashi 2019). Ostracods were marine and benthic during the Early Palaeozoic (e.g., Salas et al. 2007; Siveter 2008), colonized the water column during the Silurian (e.g., Siveter 1984; Siveter & Vannier 1990; Siveter et al. 1991; Vannier & Abe 1992) and non-marine water bodies during the Carboniferous (e.g., Williams et al. 2006; Bennett 2008; Bennett et al. 2012). Marine ostracods greatly suffered during the most devastating mass extinction at the end of the Permian about 252 Ma (see Crasquin & Forel 2014 for a summary). Ostracods from the Permian–Triassic transition have been intensively investigated since the 1970’s (e.g., Wang 1978; Shi & Chen 1987; Yi 2004; Forel et al. 2013a; Crasquin et al. 2017), allowing for the identifi cation of several survival modes in the aftermath of the crisis (e.g., Forel et al. 2013b, 2020a; Gliwa et al. 2020). Following the high amplitude diversity fl uctuations of the Early Triassic, the recovery of ostracods is considered as complete by the Anisian, Middle Triassic (e.g., Crasquin-Soleau et al. 2007; Crasquin & Forel 2014). This stage witnessed the acme of a high-diversity plateau that further developed until the brink of the end-Triassic extinction, as well as the radiation of numerous taxa, including Cytheruridae and typically Triassic ornate Bairdiidae (see Forel & Crasquin 2020 for a summary). The Triassic was also a turning point in the evolutionary history of ostracods with the replacement of the Palaeozoic evolutionary fauna by the Meso–Cenozoic one (e.g., McKenzie 1982; Crasquin-Soleau et al. 2007; Crasquin & Forel 2014).
However, this period remains enigmatic due to the temporary dominance of Platycopida, the explosive radiation of ornate Bairdiidae (e.g., Kollmann 1960, 1963; Bolz 1971a, 1971b; Kristan-Tollmann 1978) and the residual occurrence of Palaeozoic taxa in deep waters up to the Carnian, Late Triassic (e.g., Forel et al. 2019a). In that sense, the Triassic ostracod fauna is transitional as it is neither Palaeozoic, nor truly Mesozoic. One of the major future challenges of ostracodology will be to reach a stable consensus on the classifi cation of Bairdiidae, known from the Middle Ordovician (e.g., Becker 2001) up to today in all marine ecosystems, and to complete the ‘morphological phylogeny’ of Permian and Triassic ornate genera proposed by Forel & Crasquin (2020).
The Rhaetian, at the very end of the Late Triassic, witnessed the acme of several families, including Bairdiidae, Cytheruridae and Healdiidae, as well as the earliest known occurrences of Progonocytheridae and Cytheridae (Forel & Crasquin 2020). This stage precedes the end-Triassic extinction event, so the characterisation of assemblages during the Rhaetian is pivotal to providing a baseline to study this key interval. Rhaetian ostracods are known from localities in Alaska (Sohn 1987), Argentina (Ballent 1994;
Riccardi et al. 2004), Australia (Kristan-Tollmann 1986a; Dépêche & Crasquin-Soleau 1992; Kristan- Tollmann & Gramann 1992), Austria (Kollmann 1960, 1963; Kristan-Tollmann 1970, 1971a, 1971b, 1972; Bolz 1969, 1971a, 1971b; Urlichs 1972; Kristan-Tollmann et al. 1991a; Mette & Mohtat-Aghai 1999; Mette et al. 2012), Denmark (Christensen 1962), Germany (Dreyer 1967; Kozur 1968), India (Kristan-Tollmann & Gupta 1988), Iraq (Al-Khahab & Al-Halawachi 2018), Iran (Kristan-Tollmann et al. 1979, 1980), Ireland (Ainsworth & Horton 1986; Ainsworth 1989, 1990; Ainsworth et al. 1989;
Rutherford & Ainsworth 1989), Italy (Belloni 1960; Crasquin-Soleau et al. 2000), UK (Jones 1894;
Anderson 1964; Bate 1978; Boomer et al. 1999; Swift 2003) and Vietnam (Patte 1926). Here we report on the fi rst known assemblage of marine ostracods of Rhaetian age from the Romanian Black Sea shelf. The taxonomy of the marine ostracod assemblages from CM31 drill core 817LV retrieved on the Romanian Black Sea shelf is discussed, adding to the scientifi c understanding of marine ostracods during the Rhaetian stage, Late Triassic. Their taxonomy is described and discussed, including the earliest known occurrences of Pokornyopsis Kozur, 1974 as well as the youngest known record of Rectonariidae. This new material allows us to introduce the new genus Histriabairdia gen. nov. to accommodate Triassic and Jurassic species previously attributed to the extended genus Anchistrocheles Brady & Norman, 1889.
Geological and stratigraphic framework (by Eugen Grădinaru) Geological setting
The North Dobrogean Orogen apparently structurally extends eastwards into the Romanian sector of the western Black Sea shelf (Fig. 1). The Triassic rocks are widely represented in the onshore area of the North Dobrogean Orogen, with the largest areal extension and the complete stratigraphic development in the Tulcea Unit (Grădinaru 1995, 2000). However, the Triassic rocks have been found and sampled
Fig. 1. Tectonostratigraphic map of the onshore North Dobrogean Orogen showing the distribution of Triassic rocks and the location of the boreholes on the western Black Sea shelf that drilled into the Triassic. MU = Măcin Unit; CU = Consul Unit; NU = Niculițel Unit; TU = Tulcea Unit (modifi ed and completed after Grădinaru 2000). 1–4: onshore occurrences of the Rhaetian at Frecăței, Poșta, Izvoarele and Rândunica, respectively. Inset map A shows the location of the North Dobrogean Orogen. Inset map B shows the location of the study area on the western Black Sea shelf.
only in a few boreholes drilled on the Romanian Western Black Sea shelf. Grădinaru et al. (1989) provided the most complete report on the Triassic drilled in the Romanian Black Sea shelf based on the available data at that time.
The study of the Triassic rocks drilled on the Romanian Black Sea shelf is of key importance for any discussion concerning the offshore extension of the North Dobrogean Orogen. However, far too little attention has been paid in the published literature (e.g., Cătuneanu & Maftei 1994; Țambrea et al.
2002; Dinu et al. 2005) to its lithological development, microfacies features, biostratigraphy and fossil content, and to generate a well-constrained chronostratigraphic framework of the Triassic rocks drilled in the Romanian sector of the Black Sea western shelf.
The lithofacies of some Triassic rocks drilled on the Romanian western shelf of the Black Sea are comparable to those of some of the onshore North Dobrogean Triassic successions, such as those sampled in the boreholes 2 Razelm, 3 Razelm, 50 Venus or 24 Poseidon. In other cases, such as for the boreholes 814, 816 and 817 Lebăda Vest, and 30 Sinoe, the lithofacies of the sampled Triassic rocks do not match with any of the known onshore North Dobrogean Triassic successions. Apart from the two boreholes 2 Razelm and 3 Razelm, that were drilled on the shore of the Black Sea, all other boreholes are located in the area of the Histria Depression (e.g., Dinu et al. 1989, 2005).
In the present contribution, we focus on the Triassic rocks sampled in the borehole 817 Lebăda Vest (817 LV), which provides important data regarding their lithology, microfacies, and especially concerning the outstanding content of microfossils, ostracods (studied in the present paper), foraminifers (Luka Gale, pers. com.) and conodonts (Tea Kolar-Jurkovsek, pers. com.), relevant for the Rhaetian (Late Triassic) age. Macrofossils, especially brachiopods and rare bivalves, also constrain the Rhaetian age.
The borehole 817 LV was drilled into 5 m thick Triassic limestone, from 2620 to 2625 m, where it stopped (Fig. 2a). A 2 m thick drill core labelled CM31 (2623 to 2625 m) has been sampled and its ostracod content is scrutinized here. The limestone is light grey-cream in colour, compact and hard, with splintery cracking and thin veins of calcite or black clay. The last two meters of the higher core sample CM30 (2611 to 2618m) contain numerous limestone clasts, cm to dm in size, sub-angular to sub- rounded, together with clasts of volcanic origin, grey-greenish in colour, packed in slickensided Middle Jurassic black argillites.
There are several lines of evidence arguing that the Triassic drilled in the Lebada Vest fi eld is allochthonous, being represented by exotic blocks of variable sizes, from centimeters (clasts) up to tens of meters (olistoliths) embedded in Middle Jurassic dark black argillites often slickensided. The microfacially homogenous 2 m thick limestone of the drill core CM31, which doesn’t display any evident sedimentary structure, e.g., bedding, was drilled more or less along the bedding. This conclusion is also supported by the homogeneity of the ostracod assemblages retrieved from the different intervals of this drill core.
In the last decades, some authors have arbitrarily included the Romanian western Black Sea shelf in the so-called ‘Odessa Shelf’ (e.g., Okay & Tüysüz 1999; Kalvoda et al. 2002; Stephenson & Schellart 2010; Okay et al. 2015). The ‘Odessa Shelf’, in the meaning of the above-mentioned authors, is not only an incorrect geographical term but it is also not justifi ed for both geological and geopolitical reasons.
Intriguingly, the offshore extensions into the Black Sea shelf of the North Dobrogean Orogen and of the Moesian Platform, respectively, are assigned to the so-called ‘Odessa Shelf’. However, the proper Odessa Shelf is underlain solely by the East European Platform at the north and by the Scythian Platform at the south (Starostenko et al. 2015: fi g. 1), and it is fully located on the Ukraine Shelf.
There is a current tectonic model according to which the Istanbul Terrane/Zone allegedly rifted off from the Romanian/Ukrainian conjugate margin that is dubbed as the ‘Odessa Shelf’, and which was translated
Fig. 2. Lithostratigraphic log of the lowest section in the borehole 817 LV [a], showing the depth level of drill core CM31 into the allochthonous Rhaetian limestone, Romanian Western Black Sea shelf, and the position of the samples (A, B and C) investigated for ostracods; [b–g] microfacies features in the brachiopod-bearing bioclastic wackestone: [b–e] skeletal grains of calcifi ed sponge spicules and fragments of hexactinellid sponges (sp), echinoderm debris (cr), brachiopods (br), bivalves (bv), ostracods (os) and bryozoans (bry); [f] digitate cavity fi lled with micropeloidal sediment prior to the precipitation of the drusy cement – note the calcifi ed sponge spicules (sp) and foraminifers (fo);
[g] burrow infi ll with micrite containing ostracods (os).
southwards, opening the Western Black Sea basin during the Cretaceous (e.g., Okay et al. 1994, 2018;
Okay & Tüysüz 1999; Okay & Görür 2007; Tari et al. 2015; Tüysüz 2018). The Triassic succesion of the Istanbul Terrane/Zone, as described by Yurttaş-Özdemir (1971), Assereto (1972), Fantini Sestini (1988), Okay et al. (2015) and Gaetani (2016), has no counterpart, neither by its lithology nor by its ammonoid and brachiopod faunas, in the Triassic successions of any of the geological units supposedly underlying the ‘Odessa Shelf’, i.e., in the Triassic successions of the Scythian and Moesian platforms and particularly in the Triassic successions of the North Dobrogean Orogen. Moreover, the Triassic successions drilled in the Histria Depression, located in the Romanian Western Black Sea shelf in the eastward offshore prolongation of the North Dobrogean Orogen (Grădinaru et al. 1989; Cătuneanu &
Maftei 1994), are not to be found in the Istanbul Terrane/Zone.
The confusing term of the ‘Odessa Shelf’ ignores the highly differing geological structure and evolution of each of the tectonic units wrongly aggregated into it. In their suggested palaeotectonic reconstruction for the Triassic, Okay & Nikishin (2015: fi gs 6–7), to justify their assertion that the Istanbul Terrane/
Zone was the counterpart Turkish margin of the ‘Odessa Shelf’, referred to their alleged ‘Istanbul- Gebze and Dobrogea Triassic series’, in which a fully unsuitable stratigraphic column is illustrated for the Triassic of North Dobrogea. On the contrary, for the Palaeozoic, Okay & Nikishin (2015: fi g. 4) and Okay & Topuz (2017: fi g. 4) considered that the Istanbul Terrane/Zone was the counterpart of Moesia, although the Palaeozoic successions underlying the Triassic in North Dobrogea are entirely different from the Palaeozoic sedimentary series underlying the Triassic of Moesia (e.g., Seghedi 2012: fi g. 11 vs fi g.18). So, amazingly, the Istanbul Terrane/Zone is considered akin either to the North Dobrogean Orogen for the Triassic or to Moesia for the Palaeozoic, although all of these geological units have nothing in common as regards their geological history and tectonic structure. The North Dobrogean Orogen and Moesia, which were coalesced into the actual tectonic confi guration only during the Early Cretaceous, were not contiguous between them or with the Istanbul Terrane/Zone, neither in the puzzle of the Palaeozoic palaeogeography nor in that of the Triassic palaeogeography.
The dichotomy of the Triassic and Palaeozoic palaeotectonic reconstructions done by the above- mentioned authors just originates from the wrong term of the ‘Odessa Shelf’as being the supposed conjugate margin of the Istanbul Terrane/Zone.
In conclusion, the tectonic model advocating that the Western Black Sea basin opened as a back-arc basin in the Late Cretaceous separating the Pontides from mainland Eurasia (Okay et al. 2020) is completely counterproductive in any attempts to palinspastically reconstruct the palaeogeographies of the Triassic and of the Palaeozoic, respectively, for the geological units surrounding the Western Black Sea basin, as it wholly ignores the kinematic evolution of the regions lying westwards of the Black Sea (Grădinaru &
Gaetani 2019).
Microfacies and depositional environment
Microfacially, the brachiopod-bearing biomicritic limestone in the drill core of CM31 from borehole 817 LV is a burrowed bioclastic wackestone, locally a packstone. The micrite matrix, as seen in thin sections, contains predominantly skeletal grains of benthic organisms, such as sponges, echinoderm debris, brachiopods, bivalves, ostracods, foraminifers, bryozoans and rare juvenile gastropods. Skeletal particles change in frequency, but they are dominated by crinoids as well as echinoid plates and spines, to which calcifi ed sponge spicules and fragments from the fi ne skeletal network of hexactinellid sponges are added. Foraminifera are represented by rare Involutina, Ophthalmidium and encrusting ?Bullopora.
Some of the bioclasts are bioeroded, but there are abundant bioclasts that are not affected by bioerosion.
The microfacies is characterized by common burrowing and some burrows contain ostracod shells (Fig. 2b–g). Rare radiolarians are present. The micrite contains very small skeletal debris forming a fi nely bioclastic matrix. Digitate cavities are fi lled with early intrusion of the micropeloidal sediment
into cavities prior to the precipitation of drusy cement, creating normal and reverse grading and geopetal structures.
The depositional environment corresponds to a deep shelf environment that is indicated by the skeletal grains of benthic organisms. The sedimentation took place in a quiet-water, low-energy environment below the fair-weather base but within the reach of storm waves. Rare grains with ferruginous coatings indicate reworking. The diverse shelly fauna and the abundance of brachiopods and echinoderms indicate normal marine, stenohaline, well-oxygenated water conditions (cf. Flügel 2004).
Biostratigraphic data
A rich foraminiferal assemblage and rare conodonts have been obtained from residue obtained by cold acetolysis with buffered 5% acetic acid (Grădinaru et al. 1989) including Ammobaculites tzankovi (Trifonova, 1962), Cyclogyra cf. pachygyra (Gümbel, 1869), Gaudryina triassica Trifonova, 1962, G. kelleri Tappan, 1955, Gaudryinella kotlensis Trifonova, 1967, Glomospira charoides (Jones & Parker, 1860), Jaculella cf. expansa (Plummer, 1945), Oberhauserella norica Fuchs, 1968, Oberhauserellidae (diverse new species), Plagioraphe tornata Kristan-Tollmann, 1973, Pseudobolivina tornata Kristan- Tollmann, 1973, Reophax rudis Kristan-Tollmann, 1964, Tetrataxis sp., Trochammina alpina Kristan- Tollmann, 1964, Norigondolella steinbergensis (Mosher, 1968) and Oncodella paucidentata (Mostler, 1967). They are indicative of the Steinbergensis conodont biozone, base Rhaetian (Krystyn 1987).
Identifi ed brachiopods are Euxinella anatolica (Bittner, 1891), Fissirhynchia fi ssicostata (Suess, 1854) and Rhaetina pyriformis (Suess, 1854). Specimens of the bivalve Pteria? aff. gansingensis (v. Alberti, 1864) have also been retrieved.
Onshore-offshore correlation of the Rhaetian
On the onshore area of the North Dobrogean Orogen, the Upper Triassic sedimentary deposits are present only in the Tulcea Unit (Grădinaru 1995, 2000). Due to the large coverage by the Quaternary loess, the occurrences of the Upper Triassic, including here both the Norian and the Rhaetian, are scanty and limited to only a few small areas. The Rhaetian deposits are biostratigraphically documented by the coquina calcareous siltstones with Otapiria marshalli alpina Zapfe, 1973 occurring one km eastwards of Frecăței village on the right side of the Telița valley (Grădinaru 1984; Mirăuță et al. 1993). Potentially, the Rhaetian also exists in the Movila Verde hill area, westwards of Poșta village, and in the Coasta lui Nicu area, northwards of Izvoarele village, respectively, both located in the innermost part of the Tulcea Unit which is tectonically overthrusted by the Niculițel Unit (Grădinaru 1984). The Rhaetian is represented in both areas by light-grey reddish limestones and grey claystones. Crumpled reddish biomicritic limestones with Otapiria occur south of Rândunica (Congaz) village, on the left side of the Telița valley, in the same region from where Mirăuță & Gheorghian (1975) described Norian conodonts and foraminifers.
Therefore, at the present state of knowledge, the light grey-cream biomicritic limestone of drill core CM31 from borehole 817 LV has no counterpart from a lithological point of view within the Rhaetian occurring in the onshore North Dobrogean Orogen.
It is of high relevance for palaeotectonic and palaeogeographic interpretations to highlight the close lithological and palaeobiological affi nities of the allochthonous Rhaetian limestone drilled on the Romanian Black Sea shelf with the Rhaetian brachiopod-bearing biomicritic limestone within the Kichik- Sarman olistolith embedded in the Lower Eski-Orda Formation, located on the Alma-Bodrak interfl uve, east of Bakhchisaray, in the Mountainous Crimea (Korchagin et al. 2003), and also within other Crimean exotic limestone blocks (Kotlyar et al. 1999). The brachiopod fauna of the allochthonous Rhaetian limestone in drill core CM31 contains similar species to that of the allochthonous Rhaetian limestone in the Mountainous Crimea as recorded by Dagys (1974). The close affi nities of the allochthonous
Rhaetian limestone drilled on the Romanian western Black Sea shelf, in the eastwards prolongation of the North Dobrogea Orogen, with the Rhaetian limestone in the Crimean exotic blocks may open the way for constructive insights into the palaeotectonic and palaeogeographic relationships between the regions of North Dobrogea and Mountainous Crimea.
Material and methods
The studied material comes from the 2 m thick drill core CM31 (2623m to 2625m) of borehole 817 LV. Three limestone samples, labelled CM31A to CM31C (Fig. 2a), have been processed using the hot acetolysis technique (Lethiers & Crasquin-Soleau 1988; Crasquin-Soleau et al. 2005) for ostracod extraction.
In the present contribution, we follow the general classifi cation of ostracods of Moore (1961), Becker (2002) and Horne et al. (2002). The taxonomy of Cytheroidea is based on the revision of Whatley &
Boomer (2000) and that of Bythocytheridae follows Schornikov (1990).
Seventy-two species distributed across 30 genera and 13 families have been identifi ed during this investigation of drill core CM31 (Table 1). As detailed above, several taxonomic issues are still pending regarding Triassic ostracods, so all species are illustrated to enable future comparisons (Figs 5–13);
those left in open nomenclature or referred to already known species are only discussed when necessary.
In our study, most of the specimens occur as complete carapaces, which hampers the observation of internal structures on the valves. Following Maddocks (2015), the degree of slope of the antero-dorsal and postero-dorsal margins were measured on external lateral views of the carapace/valves, with 0 being horizontal. As discussed for instance in Maddocks (1969), Bairdiidae are highly homeomorphic ostracods for which diagnostic features are complex to characterize and describe. To objectivize descriptions, characters are quantifi ed as much as possible and the length convention of carapaces/valves is as follow:
< 0.40 very small, 0.40–0.50 small, 0.50–0.70 medium, 0.70–1.00 large, > 1.0 very large.
In height/length diagrams (Figs 3–4), all right and left valves are distinguished, following for instance Urlichs (1971), Harloff (1993) and Forel et al. (2020b). The accurate delimitation of ontogenetic stages in the fossil record is often diffi cult because fossil assemblages represent time-averaging of populations from different environments or seasons (e.g., Morales-Ramirez & Jakob 2008) and because the smallest (i.e., youngest) specimens are only seldomly found for diverse reasons including fossilisation, picking and identifi cation. To overcome this issue, the delineation of ontogenetic stages has been performed by producing Kernel density maps (Gaussian Kernel distribution, columns = 100, rows = 100, radius = 15 to 30) using PAST software (Hammer et al. 2001; Hammer & Harper 2005). For each species that counts at least 15 specimens (from this paper and the literature), Kernel density maps discriminate density patterns of individuals that correspond to different ontogenetical stages, with the hypothesis that the largest specimens are adults. Successive instars of ten species are recognized and described here (Figs 3–4).
Material repository
All type and fi gured specimens are deposited in the Micropalaeontology collections of the Muséum national d’histoire naturelle, Paris, France (MNHN) under catalogue numbers MNHN.F.F63181–
MNHN.F.F63331.
Anatomical abbreviations AB = anterior border ADB = antero-dorsal border AMS = adductor muscle scars AVB = antero-ventral border
Table 1 (continued on next page). Taxonomic list of all ostracod species identifi ed from drill core CM31, Black Sea, Romanian Continental Shelf, Rhaetian, Late Triassic.
Class OSTRACODA Latrielle, 1806 Subclass PODOCOPA Müller, 1894 Superfamily BAIRDIOIDEA Sars, 1887 Family BAIRDIIDAE Sars, 1887
Acratia cf. Acratia sp. A in Bolz 1971 [Fig. 5A; CM31B–C]
Acratia sp. 1 [Fig. 5B;CM31C]
Acratia sp. 2 [Fig. 3C;CM31A]
Bairdia sp. 7 in Mette & Mohtat-Aghai 1999 [Figs 5D–G;CM31 A–C]
Bairdia cf. parva Ainsworth, 1987 [Fig. 3H–I;CM31 A–C]
Bairdia sp. 3 [Fig. 5J–K; CM31 A–C]
Bairdia sp. 4 [Fig. 5L–N; CM31 A–C]
Bairdia sp. 5 [Fig. 5O–Q; CM31B–C]
Bairdia sp. 6 [Fig. 5R; CM31C]
Bairdia sp. 7 [Fig. 5S–T; CM31B]
Bairdia sp. 8 [Figs 5U, 6A; CM31B]
Bairdia sp. 9 [Fig. 6B–C; CM31C]
Bairdiacypris multidentata Bolz, 1971 [Fig. 6D–E; CM31A–B]
Bairdiacypris argonautaii Forel sp. nov. [Fig. 6F–O; CM31A–B]
Bairdiacypris sp. in Forel et al. 2018 [Fig. 6P; CM31A]
Bairdiacypris sp. 1 [Fig. 6Q; CM31A]
Bairdiacypris sp. 2 [Fig. 6R; CM31C]
Bairdiacypris sp. 3 [Fig. 6S; CM31B]
Bairdiacypris? sp. 4 [Fig. 6T–U; CM31 A–C]
Carinobairdia triassica triassica Kollmann, 1963 [Fig. 7A–B; CM31B–C]
Carinobairdia alpina Kollmann, 1963 emend. Kristan-Tollmann, 1970 [Fig. 7C–F; CM31A–C]
Ceratobairdia? akhilleusi Forel sp. nov. [Fig. 7G–S;CM31 A–C]
Ceratobairdia sp. [Fig. 7T; CM31A]
Fabalicypris cf. triassica Bolz, 1971 [Figs 7U, 8A; CM31A]
Hiatobairdia sp. 1 [Fig. 8B; CM31B–C]
Hiatobairdia sp. 2 [Fig. 8C–E; CM31B]
Hiatobairdia sp. 3 [Fig. 8F; CM31B–C]
Histriabairdia pontuseuxinusensis Forel gen. et sp. nov. [Fig. 8G–O; CM31 A–C]
Histriabairdia gen. nov. sp. 1 [Fig. 8P–R; CM31C]
Histriabairdia gen. nov. sp. 2 [Fig. 8S–U; CM31C]
Isobythocypris sp. [Fig. 9A; CM31C]
Isobythocypris atalantella Forel sp. nov. [Fig. 9B–I; CM31A–C]
Lobobairdia salinaria Kollmann, 1963 [Fig. 9J–M; CM31A–C]
Lobobairdia? sp. 1 [Fig. 9N;CM31B]
Lobobairdia sp. 2 [Fig. 9O; CM31C]
Mirabairdia sp. [Fig. 9P; CM31A]
Petasobairdia amazonella Forel sp. nov. [Figs 9Q–U, 10A–D; CM31A–C]
Superfamily BAIRDIOCYPRIDOIDEA Shaver, 1961 Family RECTONARIIDAE Gründel, 1962
Rectonariidae gen. 1 in Forel et al. 2019 [Fig. 10E; CM31C]
Superfamily CYPRIDOIDEA Baird, 1845 Family PARACYPRIDIDAE Sars, 1866
“Aglaiocypris” sp. [Fig. 10F–G; CM31A–C]
Paracypris ovidi Forel sp. nov. [Fig. 10H–N; CM31A–C]
Paracypris cf. Paracypris sp. 1 in Lord & Lambourne 1991 [Fig. 10O; CM31A]
Paracypris sp. 1 [Fig. 10P–Q; CM31A–C]
Paracypris sp. 2 [Fig. 10R–U; CM31A–C]
Paracypris sp. 3 [Fig. 11A; CM31A–B]
Table 1 (continued). Taxonomic list of all ostracod species identifi ed from drill core CM31, Black Sea, Romanian Continental Shelf, Rhaetian, Late Triassic.
Family PONTOCYPRIDIDAE Müller, 1894
Pseudomacrocypris? kerabani Forel sp. nov. [Fig. 11B–G; CM31A–C]
Pseudomacrocypris? sp. [Fig. 11H; CM31B–C]
Superfamily CYTHEROIDEA Baird, 1850 Family BYTHOCYTHERIDAE Sars, 1866
Praebythoceratina sp. [Fig. 11I–J; CM31B–C]
Triassocythere sp. [Fig. 11K; CM31C]
Family CYTHERURIDAE Müller, 1894 Subfamily CYTHERURINAE Müller, 1894
Judahella andrusovi Kozur & Bolz in Bunza & Kozur, 1971 [Fig. 11L–M; CM31A–C]
Cytheruridae gen. et sp. indet. [Fig. 11N–P; CM31B–C]
Superfamily MACROCYPRIDOIDEA Mü ller, 1912 Family MACROCYPRIDIDAE Sars, 1866
Praemacrocypris sp. [Fig. 11Q; CM31B]
Superfamily SIGILLIOIDEA Mandelstam, 1960 Family SIGILLIIDAE Mandelstam, 1960
Cardobairdia sp. 1 [Fig. 11R–S; CM31A–B]
Cardobairdia sp. 2 [Figs 11T–U, 12A-C; CM31A–C]
Cardobairdia sp. 3 [Fig. 12D–F; CM31A, C]
Cardobairdia sp. 4 [Fig. 12G–K; CM31A–B]
Cardobairdia sp. 5 [Fig. 12L; CM31C]
Cardobairdia? sp. 6 [Fig. 12M; CM31B]
Suborder METACOPINA Sylvester-Bradley, 1961 Superfamily HEALDIOIDEA Harlton, 1933 Family HEALDIIDAE Harlton, 1933
Hungarella koessenensis (Mette & Mohtat-Aghai, 1999) [Fig. 12N–Q; CM31A–C]
Hungarella sp. 1 [Fig. 12R; CM31B]
Hungarella? sp. 2 [Fig. 12S; CM31C]
Order PLATYCOPIDA Sars, 1866 Suborder PLATYCOPINA Sars, 1866 Superfamily CYTHERELLOIDEA Sars, 1866 Family CYTHERELLIDAE Sars, 1866
Cytherelloidea cf. modesta Apostolescu, 1959 [Fig. 12T; CM31B–C]
Cytherelloidea? sp. [Fig. 12U; CM31A]
Leviella sp. [Fig. 13A; CM31C]
Subclass MYODOCOPA Sars, 1866 Order HALOCYPRIDA Dana, 1853 Suborder HALOCYPRIDINA Dana, 1853
Superfamily THAUMATOCYPRIDOIDEA Mü ller, 1906 Family THAUMATOCYPRIDIDAE Müller, 1906
Pokornyopsis sp. 1 [Fig. 13B–C; CM31B]
Pokornyopsis? sp. 2 [Fig. 13D–E; CM31A]
Pokornyopsis sp. 3 [Fig. 13F; CM31A]
Order MYODOCOPIDA Sars, 1866 Suborder MYODOCOPINA Sars, 1866
Superfamily CYLINDROLEBERIDOIDEA Mü ller, 1906 Family CYLINDROLEBERIDIDAE Mü ller, 1906
Hungaroleberis sp. 1 [Fig. 13G–I; CM31A–C]
Hungaroleberis sp. 2 [Fig. 13J–L; CM31A]
Superfamily POLYCOPOIDEA Sars, 1866 Family POLYCOPIDAE Sars, 1866
Polycope sp. 1 [Fig. 13M; CM31A–C]
Polycope sp. 2 [Fig. 13N; CM31A–C]
Polycope sp. 3 [Fig. 13O; CM31A–B]
Polycope sp. 4 [Fig. 13P; CM31C]
Fig. 3. Height/length scatter plots of species from borehole 817 Lebăda Vest, drill core CM31, western portion of Black Sea shelf, Rhaetian, Late Triassic. In all diagrams, the dimensions of right (stars) and left (circles) valves of complete carapaces are shown separately and circled or linked. P1 = paratype 1;
P2 = paratype 2. A. Bairdiacypris multidentata Bolz, 1971. B. Bairdiacypris argonautaii Forel sp. nov.
C. Carinobairdia alpina Kollmann, 1963. D. Ceratobairdia? akhilleusi Forel sp. nov. E. Histriabairdia pontuseuxinusensis Forel gen. et sp. nov. F. Isobythocypris atalantella Forel sp. nov. G. Petasobairdia amazonella Forel sp. nov. H. Paracypris ovidi Forel sp. nov.
DB = dorsal border H = height L = length LV = left valve PB = posterior border PDB = postero-dorsal border PVB = postero-ventral border RV = right valve
VB = ventral border W = width
Results
Systematic palaeontology (by Marie-Béatrice Forel)
Class Ostracoda Latreille, 1806 Subclass Podocopa Müller, 1894 Superfamily Bairdioidea Sars, 1887
Family Bairdiidae Sars, 1887 Subfamilial and generic discussions
Taxonomy of Bairdiidae: state of the art and consensus
Bairdiidae have been components of marine ostracod assemblages from the Ordovician (e.g., Moore 1961; Salas 2007) to present days (e.g., Brady 1880, 1890; Maddocks 1969, 1975; Titterton & Whatley 1988; Brandão 2008). Their generally simple and smooth carapaces make it complex to accurately discriminate taxa and describe their diagnostic characters. This homeomorphy led to the unreliability of their taxonomy, as has often been discussed in the literature (e.g., Maddocks 1969; Malz 1988).
Intense efforts have partly clarifi ed the taxonomy of modern representatives of the ‘Bairdia dynasty’
(Malz 1988) with the establishment and/or revision of Neonesidea Maddocks, 1969, Paranesidea Maddocks, 1969, Bairdoppilata Coryell et al., 1935 and Triebelina van den Bold, 1946 (e.g., Maddocks
Fig. 4. Height/length scatter plots of species from borehole 817 Lebăda Vest, drill core CM31, western portion of Black Sea shelf, Rhaetian, Late Triassic. In all diagrams, the dimensions of right (stars) and left (circles) valves of complete carapaces are shown separately and circled or linked. A. Pseudomacrocypris?
kerabani Forel sp. nov. B. Hungarella koessenensis (Mette & Mohtat-Aghai, 1999).
1969, 2013, 2015). The diagnostic features of these genera are found in soft parts as well as carapaces, and recently the taxonomic potential of their chewing apparatus has been discussed (Maddocks 2013, 2018). Conversely, the classifi cation of fossil Bairdiidae has not improved much since the 1960’s, when Sohn (1960) and Kollmann (1960, 1963) clarifi ed the classifi cation of Palaeozoic and Triassic taxa, respectively. Although the taxonomic conclusions of these papers are disputed, it is agreed that Bairdia s. str. is restricted to the Palaeozoic and that “to include other forms under this name violates its morphologic and quite possibly its phyletic homogeneity” (Maddocks 1969: 1). Maddocks (1969) and all subsequent contributions deconstructed the widespread idea, termed ‘heresy’, that “the ‘key’
to relationships among Recent ostracod species is to be found in the soft parts, and that the carapace alone provides insuffi cient evidence for distinction of ‘biologic’ or ‘natural’ taxa”. In the long evolutionary history of Bairdiidae, the Triassic period has been a turning point in recording the explosive diversifi cation of ornate forms (e.g., Kollmann 1960, 1963; Kristan-Tollmann 1970, 1971a; Bolz 1971a, 1971b; Kozur 1971a, 1971b) that are still present in modern marine ecosystems, although less abundant and diverse (e.g., Brady 1870; Cabioch et al. 1986; Malz & Lord 1988; Titterton & Whatley 1988; Jellinek 1989; Maddocks & Wouters 1990; M.-B. Forel, pers. obs. and work in progress). The classifi cation of fossil and recent ornate Bairdiidae, defi ned as “small to medium-sized, thick-shelled, heavily ornamented forms, largely but not entirely restricted to reefal habitats” (Maddocks & Wouters 1990: 173), has been debated since their descriptions, as was summarized for instance in Bolz (1971a, 1971b). Notwithstanding the problems we have encountered, we consider that it is beyond the scope and intention of this paper and its material to attempt a revision of the Bairdiidae at the subfamilial and generic levels. An attempt to introduce a phylogeny for Permian and Triassic genera has recently been proposed, describing two lineages (Ceratobairdia lineage and Abrobairdia lineage), both derived from Petasobairdia in the early Permian (Forel & Crasquin 2020). Until this model is improved, we follow the generic scheme of Kollmann (1963) in considering primary ornamentation as a relevant generic character, considering that ornamentation is widely used as a generic marker, mutatis mutandis, for other families (e.g., Trachyleberididae: Moore 1961; Warne & Whatley 2016) and often corresponds to morphologic features with diverse functions, some of which are genetically controlled (e.g., Liebau 1977; Keyser 1995). We furthermore follow the subfamilial scheme proposed by Maddocks (1969) in which most of the Triassic subfamilies created in the successive contributions of Kollmann and Kristan- Tollmann are downgraded to the tribe level. We consider this inclusive scheme as the most reasonable to avoid artifi cial over-splitting.
Taxonomic consensus on Bairdiacypris / Fabalicypris / Isobythocypris
The original description of Fabalicypris Cooper, 1946 states that it is morphologically close to other bairdiids but differs from Bairdia McCoy, 1844 and Bairdiacypris Bradfi eld, 1935 in lacking a pronounced postero-dorsal slope and highly arched dorsal border. It is further differentiated from Bairdia by the lack of an acuminate posterior end. Fabalicypris also differs from Bairdiacypris in being more tumid and by the presence of a pronounced offset of the antero-ventral overlap (Cooper 1946).
These elements are problematic, as they imply that Bairdia and Bairdiacypris should also differ by the presence of an antero-ventral overlap in Bairdia, which is not the case. In subsequent years, the validity of Fabalicypris has been discussed, leading to different schools of thought. The fi rst one considers that the characters differentiating Bairdiacypris and Fabalicypris are highly variable and that Fabalicypris is a junior synonym of Bairdiacypris (e.g., Sohn 1983; Hoare et al. 1999). The second school of thought considers Fabalicypris as a subgenus of Bairdiacypris, described as “with overall carapace morphology of Bairdiacypris, but bairdiid shape more or less obscured; ventral overlap decreasing abruptly in anterior third to form offset or step-like process” (Becker 2001). Conversely, Bairdiacypris is described as
“elongate bairdiid outline; dorsal margin tripartite, sometimes barely discernible; posterior end rounded”
(Becker 2001). Here, we follow the fi rst school of thought to avoid complicating the taxonomic situation of bairdiids until a complete revision of these ostracods. We therefore use the following diagnostic summaries provided by Ainsworth (1990):
Bairdiacypris: “Carapace of medium to large size, subovate to subtriangular, laterally compressed in dorsal view. Anterior margin asymmetrically rounded, lower margin convex, upper margin straight.
Posterior margin broadly rounded. Dorsal margin near straight to strongly arched. Ventral margin often with a well formed oral concavity in right valve. Hinge adont, short. Inner lamella moderately wide, with both anterior and posterior vestibules. Muscle scar pattern of several discrete spots” (Ainsworth 1990: 179).
Fabalicypris: “Carapace of medium to large size, elongate subovate to elongate subtriangular in lateral view. Anterior margin rounded. Posterior margin strongly asymmetrically rounded, near subtriangular.
Dorsal margin generally evenly arched. Ventral margin straight, with a prominent oral concavity in right valve. Inner lamella moderately wide. Hinge adont” (Ainsworth 1990: 179).
Confusion may also arise for the distinction of Isobythocypris Apostolescu, 1959 from other bairdiids.
The diagnosis of Isobythocypris is as follows: “Un genre de Bairdiidae caractérisé par sa carapace subréniforme et par sa charnière. Dans la valve droite, le système de fermeture consiste en deux proéminences de forme elliptique; dans la valve gauche, un sillon étroit et lisse, terminé à chaque extrémité par un alvéole” (Apostolescu 1959 : 807), which translates as “a genus of Bairdiidae characterized by its subreniform carapace and its hinge. In the right valve, the closing system consists of two elliptical protuberances; in the left valve, a narrow and smooth ridge, terminated by an alveole at each extremity”.
Ainsworth (1989, 1990) clarifi ed the diagnosis of Isobythocypris as follows: “Carapace of medium to large size, subrectangular to elongate subrectangular. Inner lamella broad, especially anteriorly. Anterior and posterior vestibules moderately wide. Hinge lophodont” (Ainsworth 1989: 126, 1990: 179). In the present investigation, most of the specimens are present as complete carapaces or as valves with poorly preserved inner surface so that hingement was not accessible. The outer characters used here to distinguish Bairdiacypris, Fabalicypris and Isobythocypris are summarized in Table 2.
Subfamily Bairdiinae Sars, 1923 Genus Acratia Delo, 1930 Type species
Acratia typica Delo, 1930, by original designation.
Acratia cf. Acratia sp. A in Bolz 1971 Fig. 5A
Material examined
ROMANIA • 1 complete carapace; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63181 • 1 LV; same locality as for preceding but sample CM31C; Rhaetian, Upper Triassic; MNHN.F.F63341.
Table 2. Classifi cation consensus for Bairdiacypris Bradfi eld, 1935, Fabalicypris Cooper, 1946 and Isobythocypris Apostolescu, 1959.
Lateral outline Dorsal margin Ventral offset
Bairdiacypris subovate-subtriangular tripartite absent
Fabalicypris elongate subovate-elongate subtriangular arched present Isobythocypris subrectangular-elongate subrectangular arched absent
Dimensions
Bolz (1971b) provided measurements for two carapaces and a RV. Here we equate the measurements of carapaces with those of the larger LV to allow for comparisons (Table 3).
Occurrence
Romanian Continental Shelf, Black Sea, Rhaetian, Late Triassic (this paper).
Remarks
This species differs from Acratia sp. A in Bolz 1971b from the Norian–Rhaetian of the Northern Calcareous Alps (Bolz 1971b) in being slightly more elongate, having a more pronounced ventral concavity, a more angulate dorsal margin at LV and a rostrum located higher. The two species are nevertheless close morphologically as shown by the antero-dorsal offset of LV over RV. The complete carapace recovered here is slightly smaller than the specimens reported from Austria (Table 3) and could represent an immature juvenile. We cannot exclude that the observed differences relate to ontogeny, the antero-dorsal offset being a diagnostic character of the species. Acratia cf. Acratia sp. A in Bolz 1971 is also close to A. goemoeryi Kozur, 1970 from the Middle Triassic of Hungary (Kozur 1970). Forel et al.
(2019a) plotted the H/L diagram of all known specimens of A. goemoeryi, in which the present specimen could correspond to a relatively young juvenile stage. Several isolated valves or poorly preserved carapaces of A. goemoeryi have been documented from the Middle Triassic and early Late Triassic, which do not allow for the observation of the possible dorsal offset visible in Acratia sp. A in Bolz 1971 and Acratia cf. Acratia sp. A in Bolz 1971. Furthermore, the ADB of RV is arched in A. goemoeryi while it is concave in the present material.
Acratia sp. 1 Fig. 5B Material examined
ROMANIA • 1 RV; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31C; Rhaetian, Upper Triassic; MNHN.F.F63182.
Dimensions
L = 343 μm; H = 147 μm; H/L = 0.43.
Occurrence
Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Table 3. Dimensions of all specimens of Acratia cf. Acratia sp. A in Bolz 1971 (this paper).
Length (μm) Height (μm) H/L Reference
A. sp. A (LV) 1590 610 0.38 Bolz (1971b)
A. sp. A (LV) 1110 450 0.40 Bolz (1971b)
A. sp. A (RV) 1380 550 0.40 Bolz (1971b)
A. cf. A. sp. A
(LV of carapace) 828 291 0.35 This paper
A. cf. A. sp. A
(RV of carapace) 828 280 0.34 This paper
Remarks
The small dimensions of this specimen indicate that it may be an immature stage. However, its very rounded anterior margin and downward pointing posterior extremity preclude it from being attributed to any of the co-occurring species of Acratia. Acratia sp. 1 is close to Paracypris sp. 1 in Lord &
Lambourne 1991 from the Early Jurassic of Turkey (Lord & Lambourne 1991) and to Paracypris cf.
Paracypris sp. 1 in Lord & Lambourne 1991 in the present paper (Fig. 10O). However, the small antero- ventral concavity of the present specimen relates it to the genus Acratia. Acratia sp. 1 is also related to A. kollmanni Forel in Forel et al., 2019 from the Carnian, Late Triassic, of Turkey (Forel et al. 2019a) as shown by its anterior and posterior extremities being located very low, with a uniformly rounded dorsal margin. However, A. kollmanni is shorter and higher and has a more incised antero-ventral concavity.
Genus Bairdia McCoy, 1844 Type species
Bairdia curta McCoy, 1844, subsequently designated by Ulrich & Bassler (1923).
Bairdia sp. 7 in Mette & Mohtat-Aghai 1999 Fig. 5D–G
Bairdia sp. 7 – Mette & Mohtat-Aghai 1999: pl. 4, fi gs 4–5.
Material examined
ROMANIA • 1 RV; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63184 • 1 RV; same locality as for preceding but sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63185 • 1 LV; same locality as for preceding but sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63186 • 2 complete carapaces, 5 RV, 4 LV; same locality as for preceding but samples CM31A, CM31B and CM31C; Rhaetian, Upper Triassic; MNHN.F.F63342.
Fig. 5 (opposite page). SEM micrographs of ostracods from borehole 817 Lebăda Vest, drill core CM31, western portion of Black Sea shelf, Rhaetian, Late Triassic. All specimens are housed in the collections of the Muséum national d’histoire naturelle, Paris, France (MNHN). A. Acratia cf. Acratia sp. A in Bolz 1971, right lateral view of a carapace, sample CM31B (MNHN.F.F63181). B. Acratia sp. 1, external view of a right valve, sample CM31C (MNHN.F.F63182). C. Acratia sp. 2, right lateral view of a carapace, sample CM31A (MNHN.F.F63183). D–G. Bairdia sp. 7 in Mette & Mohtat-Aghai 1999. D. External view of a right valve, sample CM31B (MNHN.F.F63184). E. External view of a right valve, sample CM31A (MNHN.F.F63185). F. External view of a left valve, sample CM31B (MNHN.F.F63186). G. Same specimen, inner view. H–I. Bairdia cf. parva Ainsworth, 1987. H. Right lateral view of a carapace, sample CM31B (MNHN.F.F63187). I. Right lateral view of a carapace, sample CM31B (MNHN.F.F63188). J–K. Bairdia sp. 3. J. Right lateral view of a carapace, sample CM31A (MNHN.F.F63189). K. Right lateral view of a carapace, sample CM31C (MNHN.F.F63190).
L–N. Bairdia sp. 4. L. Right lateral view of a carapace, sample CM31C (MNHN.F.F63191). M. Right lateral view of a carapace, sample CM31B (MNHN.F.F63192). N. Same specimen, dorsal view.
O–Q. Bairdia sp. 5. O. Right lateral view of a carapace, sample CM31C (MNHN.F.F63193). P. Same specimen, dorsal view. Q. Right lateral view of a carapace, sample CM31B (MNHN.F.F63194).
R. Bairdia sp. 6, external view of a left valve, sample CM31C (MNHN.F.F63195). S–T. Bairdia sp.
7. S. Right lateral view of a carapace, sample CM31B (MNHN.F.F63196). T. Same specimen, dorsal view. U. Bairdia sp. 8, right lateral view of a carapace, sample CM31B (MNHN.F.F63197). Scale bars:
100 μm.
Dimensions (this paper)
RV: L = 372–1138 μm; H = 200–603 μm; H/L = 0.53–0.56.
LV: L = 372–1212 μm; H = 205–768 μm; H/L = 0.55–0.63.
Occurrence
Kössen Formation, Northern Calcareous Alps, Tyrol, Austria, Rhaetian, Upper Triassic (Mette & Mohtat- Aghai 1999); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
Bairdia sp. 7 in Mette & Mohtat-Aghai 1999 was fi rst recorded from the Kössen Formation outcropping in the Northern Calcareous Alps (Mette & Mohtat-Aghai 1999). This species is higher and slightly shorter than B. cassiana (Reuss, 1869), which is largely documented from the Early Anisian–Late Carnian interval of Europe (Reuss 1869; Gümbel 1869; Styk 1958; Urlichs 1972; Kristan-Tollmann 1978; Kristan-Tollmann et al. 1991b; Monostori 1995; Crasquin-Soleau & Grădinaru 1996; Monostori &
Tóth 2013, 2014; Mette et al. 2015; Crasquin et al. 2018; Forel et al. 2020). It also shares morphological proximity with B. jiangyouensis Xie in Wei et al., 1983 from the Carnian–Norian interval of Sichuan Province, South China (Wei et al. 1983; Forel et al. 2019b), from which it differs by a larger and slightly less caudate posterior end and an anterior maximum of convexity located lower. Bairdia jiangyouensis is also characterized by having LV overlapping RV all around: the nature of the overlap cannot be completely characterized for the present species as only juvenile carapaces have been found, with an interrupted overlap along AVB and AB. Bairdia sp. 7 in Mette & Mohtat-Aghai 1999 also differs from Bairdia sp. A in Bolz 1971 from the Zlambach Formation, Norian–Rhaetian, of the Northern Calcareous Alps (Bolz 1971a: pl. 7, fi gs 82–83) in having a tripartite dorsal margin on RV, while it is uniformly convex in Bairdia sp. A. It also differs from Bairdia sp. B in Bolz 1971 (Bolz 1971a: pl. 7, fi gs 82–83) by having its DB inclined posteriorly, PB larger and less caudate and AVB less convex and anteriorly projected. It is also close to Bairdia sp. in Kristan-Tollmann 1979 from the Rhaetian of Iran (Kristan-Tollmann et al. 1979), but the RV of the Iranian species has a shorter posterior end, a pronounced concavity at the ADB and a slight concavity at the base of the AVB. Crasquin et al. (2018) recently considered that Bairdia sp. 3 from the Carnian, Late Triassic, of Sicily (Crasquin et al. 2018:
fi g. 6u) might be conspecifi c with Bairdia sp. 7 in Mette & Mohtat-Aghai 1999. However, the specimen shown in Crasquin et al. (2018) has a longer and more caudate posterior border, with AVB and PVB slightly compressed laterally in their median extremity. For this reason, we do not consider these taxa to be conspecifi c. Bairdia sp. 7 in Mette & Mohtat-Aghai 1999 is undeniably new to science, but it is kept in open nomenclature until complete carapaces are discovered to fully describe the overlap of the LV over RV. The description of the ontogeny of the species listed above will allow the clarifi cation of their possible conspecifi cities, but until now most of them are only know from a few specimens.
Genus Bairdiacypris Bradfi eld, 1935 Type species
Bairdiacypris deloi Bradfi eld, 1935, by original designation.
Bairdiacypris multidentata Bolz, 1971 Fig. 6D–E
Bairdiacypris multidentata Bolz, 1971b: 230–231, pl. 8, fi gs 98–100.
Bairdiacypris multidentata – Mette et al. 2012: 70.
Material examined
ROMANIA • 1 complete carapace; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63199 • 1 complete carapace; same locality as for preceding but sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63200 • 1 broken carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63343.
Dimensions See Fig. 3A.
Occurrence
Northern Calcareous Alps, Tyrol, Austria, Norian–Rhaetian, Upper Triassic (Bolz 1971b; Mette et al.
2012); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
Bairdiacypris cf. multidentata Bolz, 1971 has been reported from the Eiberg Member, Kössen Formation, outcropping at the Eiberg section in the Northern Calcareous Alps (Mette et al. 2012: 70), but no illustration and no discussion were provided to further discuss this attribution. Bolz (1971b) provided dimensions of complete carapaces, LV and RV: owing to the overlap of LV over RV in B.
multidentata, the dimensions of carapaces are here treated as those of LV and all dimensions are plotted in Fig. 3A. Bolz (1971b) illustrated three specimens and stated that the material was not suffi cient for an investigation of the ontogeny (Bolz 1971b: 231). Although the lack of illustrated specimens doesn’t allow a discussion of the morphological changes in B. multidentata through its development, the large dispersion of the H/L scatter plot of all specimens points to a mixture of ontogenetic stages, at least corresponding to fi ve ontogenetic stages (A-4 to adult). The holotype appears to be an immature stage. The only measurable carapace found during the present analysis (Fig. 6E) is the smallest known carapace of B. multidentata and corresponds to a very young juvenile in the A-4 stage (Fig. 3A).
Bairdiacypris argonautaii Forel sp. nov.
urn:lsid:zoobank.org:act:4AF32BE0-8E7A-4ABD-BCC8-42D2F99F451F Fig. 6F–O
Bairdiacypris? aff. Bairdiacypris sp. A Bolz – Mette & Mohtat-Aghai 1999: pl. 3, fi g. 7.
Diagnosis
A new species ovoid in shape, with overlap interrupted at AVB and PVB, RV preplete and LV amplete to postplete.
Etymology
From the ancient Greek Αργοναῦται, Argonautai, referring to the mythological heroes, the argonauts, who travelled the Black Sea searching for the golden fl eece.
Material examined Holotype
AUSTRIA • 1 RV; Northern Calcareous Alps, Tyrol; Kössen Formation, Rhaetian, Upper Triassic (Mette & Mohtat-Aghai 1999: pl. 3, fi g. 7); University of Innsbruck, Austria.
Paratypes
ROMANIA • 1 RV; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63201 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63202.
Other material
ROMANIA • 1 complete carapace; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63203 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63204 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63206 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63207 • 1 complete carapace; same locality as for preceding but sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63205 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63208.
Dimensions See Fig. 3B.
Description
CARAPACE. Very large, massive, ovoid in lateral view with Lmax below mid-H at both valves; LV larger than RV, overlapping it all along dorsal margin with maximum at DB, and along VB, overlap interrupted along AVB and PVB; biconvex in dorsal view with Wmax behind Lmax, overlapping area seemingly fl at;
surface smooth.
RV. Subrectangular with Hmax at antero-dorsal angulation; dorsal margin tripartite with dulled angulations;
PDB straight to slightly convex in young instars, short (12–21% of Lmax) and steeply sloping to PB (60–70°); DB straight, moderately sloping to postero-dorsal angulation (10–20°) with length increasing through ontogeny; ADB straight, long, with relatively constant length through ontogeny (37–45% of L), sloping toward AB with an angle ranging from 20° to 40°; AB large, relatively bairdiid in shape, with maximum of curvature at or slightly below mid-H; ventral margin long and sinuous; AVB steeply raised Fig. 6 (opposite page). SEM micrographs of ostracods from borehole 817 Lebăda Vest, drill core CM31, western portion of Black Sea shelf, Rhaetian, Late Triassic. All specimens are housed in the collections of the Muséum national d’histoire naturelle, Paris, France (MNHN). A. Bairdia sp. 8, same specimen as in Fig. 5U, dorsal view. B–C. Bairdia sp. 9. B. Right lateral view of a carapace, sample CM31C (MNHN.F.F63198). C. Same specimen, dorsal view. D–E. Bairdiacypris multidentata Bolz, 1971. D. Right lateral view of a carapace, sample CM31A (MNHN.F.F63199). E. Right lateral view of a carapace, sample CM31B (MNHN.F.F63200). F–O. Bairdiacypris argonautaii Forel sp. nov.
F. Paratype 2, right lateral view of a carapace, sample CM31A (MNHN.F.F63201). G. Paratype 1, external view of a right valve, sample CM31B (MNHN.F.F63202). H. Right lateral view of a carapace, sample CM31A (MNHN.F.F63203). I. Right lateral view of a carapace, sample CM31A (MNHN.F.F63204).
J. Right lateral view of a carapace, sample CM31B (MNHN.F.F63205). K. Same specimen, dorsal view.
L. Right lateral view of a carapace, sample CM31A (MNHN.F.F63206). M. Right lateral view of a carapace, sample CM31A (MNHN.F.F63207). N. Same specimen, dorsal view. O. Right lateral view of a carapace, sample CM31A (MNHN.F.F63208). P. Bairdiacypris sp. in Forel et al. 2018, external view of a right valve, sample CM31A (MNHN.F.F63209). Q. Bairdiacypris sp. 1, external view of a right valve, sample CM31A (MNHN.F.F63210). R. Bairdiacypris sp. 2, external view of a right valve, sample CM31C (MNHN.F.F63211). S. Bairdiacypris sp. 3, external view of a right valve, sample CM31B (MNHN.F.F63212). T–U. Bairdiacypris? sp. 4. T. Right lateral view of a carapace, sample CM31B (MNHN.F.F63213). U. Right lateral view of a carapace, sample CM31A (MNHN.F.F63214). Scale bars: 100 μm.
to AB and largely convex to close to vertical in young instars; VB with tenuous oral concavity mid-L;
PVB short, convex, only slightly raised to PB; PB at lower ¼ of Hmax, relatively narrow, gently rounded to only slightly bairdiid in shape.
LV. Ovoid with Hmax behind mid-H in large forms, at antero-dorsal angulation in younger instars; dorsal margin gently rounded with dulled angulations in young instars that are unrecognizable in larger instars and adults; ventral margin long and straight to gently convex.
Occurrence
Kössen Formation, Northern Calcareous Alps, Tyrol, Austria, Rhaetian, Upper Triassic (Mette & Mohtat- Aghai 1999); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
Bairdiacypris argonautaii sp. nov. is higher and shorter than “Bairdia” raetica Bolz, 1971 from the Rhaetian interval, Late Triassic, of Tyrol (Bolz 1971b); it also differs by the antero-ventral and postero-ventral interruption of the overlap, dorsal margin tripartite with pronounced antero-dorsal and postero-dorsal angulations and anterior margin larger. Bairdiacypris argonautaii sp. nov. is also close to Bairdiacypris sp. in Kristan-Tollmann et al. 1979 from the Rhaetian, Late Triassic, of Iran (Kristan- Tollmann et al. 1979) but the only illustrated Iranian specimen shows a continuous overlap along AVB and PVB and a posterior maximum of convexity located higher resulting in subsymmetric anterior and posterior borders. Bairdiacypris argonautaii sp. nov. is also morphologically close to Bairdia cf.
peneovoidea Bolz, 1971 from the Rhaetian, Late Triassic, of Iran (Kristan-Tollmann et al. 1979) but has a more rounded AVB and a larger PB. The dimensions of all specimens attributed to B. argonautaii sp. nov.
are plotted in Fig. 3B. The largest specimen known to date is a right valve from the Rhaetian of Tyrol (Mette & Mohtat-Aghai 1999). All specimens found in the present investigation are distributed across at least six successive ontogenetic stages, all smaller than the specimen from Mette & Mohtat-Aghai (1999). The ontogenetic development of B. argonautaii sp. nov. is mainly marked by an enlargement of the posterior end of the carapace.
Bairdiacypris sp. in Forel et al. 2018 Fig. 6P
Bairdiacypris sp. – Forel et al. 2018: fi g. 4/16.
Material examined
ROMANIA • 1 RV; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63209.
Dimensions
RV in Forel et al. (2018): L = 774 μm; H = 320 μm; H/L = 0.41.
RV in this paper: L = 766 μm; H = 331 μm; H/L = 0.43.
Occurrence
Killik Formation, Tavusçayiri Block, Sorgun Ophiolitic Mélange, southern Turkey, Huğlu Tuffi te, Spongotortilispinus moixi radiolarian Zone, lower Tuvalian, Upper Carnian, Upper Triassic (Forel et al.
2018); Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
Bairdiacypris sp. in Forel et al. 2018 is related to Bairdiacypris anisica Kozur, 1971 from the Anisian, Middle Triassic, of Hungary (Kozur 1971c). However, only one valve has been found here; since bairdiids are very homoplastic ostracods, it is most reasonable to avoid artifi cially extending the
stratigraphic range of Bairdiacypris anisica Kozur, 1971, from the Middle Triassic to the end of the Rhaetian, until more material is available to clarify this possibility. Bairdiacypris sp. in Forel et al.
2018 is also morphologically close to Bairdiacypris sp. in Forel et al. 2019 from the Carnian, Late Triassic, of the Kilek section in Turkey (Forel et al. 2019a), but the anterior border is more raised in the present material. In the present analysis, Bairdiacypris sp. in Forel et al. 2018 is primarily related to Bairdiacypris sp. 1, from which it differs mainly by the morphology of the posterior extremity and the position of the oral concavity in front of Hmax, while it is at mid-L in Bairdiacypris sp. 1.
Bairdiacypris sp. 1 Fig. 6Q Material examined
ROMANIA • 1 RV; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63210.
Dimensions
L = 821 μm; H = 311 μm; H/L = 0.38.
Occurrence
Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
Bairdiacypris sp. 1 differs from Bairdiacypris sp. in Forel et al. 2018 in being more elongate in lateral view with a more elongate posterior end, PB located higher and PDB concave, while it is uniformly convex in Bairdiacypris sp. in Forel et al. 2018. Bairdiacypris sp. 1 is also close to Fabalicypris triassica Bolz, 1971 from the Norian–Rhaetian of the Northern Calcareous Alps (Bolz 1971b), but it differs by its higher posterior end and straight DB. In spite of the lack of a complete carapace to observe the nature of its ventral overlap, Bairdiacypris sp. 1 has a clear tripartite dorsal margin, which precludes the attribution to Fabalicypris.
Bairdiacypris sp. 3 Fig. 6S Material examined
ROMANIA • 1 RV; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63212 • 1 complete carapace; same collection data as for preceding; Rhaetian, Upper Triassic; MNHN.F.F63344.
Dimensions
L = 1060 μm; H = 481 μm; H/L = 0.45.
Occurrence
Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
Bairdiacypris sp. 3 is close to Fabalicypris n. sp. in Kristan-Tollmann et al. 1980 from the Rhaetian of Iran (Kristan-Tollmann et al. 1980), but the present species has a tripartite dorsal margin at RV
with longer DB and lacks the Fabalicypris offset of the ventral overlap. Bairdiacypris sp. 3 is also close to Bairdiacypris? sp. 2 in Lord & Lambourne 1991 from the Pliensbachian, Early Jurassic, of Turkey (Lord & Lambourne 1991), from which it differs in being larger with a less elongate posterior end. Bairdiacypris sp. 3 shares a strong similarity with Bairdiacypris sp. B in Bolz 1971 from the Rhaetian interval of the Northern Calcareous Alps (Bolz 1971b), which is only shown as inner views.
However, Bairdiacypris sp. 3 has a shorter DB and a larger PB with maximum of convexity located higher. Bairdiacypris sp. 3 is also larger than Bairdiacypris sp. B in Bolz 1971 (L = 690–950 μm;
H = 320–500 μm; H/L = 0.44–0.55), with a similar H/L ratio; this characteristic could relate to ontogeny.
It is nevertheless worth noting that the H/L ratio of Bairdiacypris sp. B in Bolz 1971 mainly ranges from 0.44 to 0.48 (Bolz 1971b: 231). The dimensions provided for the specimen illustrated in Bolz (1971b:
pl 8, fi g. 104) are L = 900 μm and H = 500 μm, leading to an H/L ratio of 0.55.
Bairdiacypris? sp. 4 Fig. 6T–U Material examined
ROMANIA • 1 complete carapace; Black Sea, Romanian Continental Shelf, borehole 817LV, sample CM31B; Rhaetian, Upper Triassic; MNHN.F.F63213 • 1 complete carapace; same locality as for preceding but sample CM31A; Rhaetian, Upper Triassic; MNHN.F.F63214 • 5 complete carapaces;
same locality as for preceding but samples CM31A, CM31B and CM31C; Rhaetian, Upper Triassic;
MNHN.F.F63345.
Dimensions
RV: L = 327–809 μm; H = 157–326 μm; H/L = 0.38–0.48.
LV: L = 327–809 μm; H = 167–348 μm; H/L = 0.41–0.51.
Occurrence
Romanian Continental Shelf, Black Sea, Rhaetian, Upper Triassic (this paper).
Remarks
The absence of an antero-ventral offset of the overlap leads to the generic attribution to Bairdiacypris rather than Fabalicypris. However, in the absence of angulations at the dorsal margin, this identifi cation is still tentative. Bairdiacypris? sp. 4 is closely related to Fabalicypris? praelonga Donze, 1966 from the Plicatulus Horizon, Hettangian, Early Jurassic, of Le Sartre, Ardèche, France (Donze 1966). However, Bairdiacypris? sp. 4 differs by having a more bairdiid AB with a maximum of curvature located higher and the AVB more raised dorsally. It is worth noting that the doubt in the generic attribution of Fabalicypris? praelonga is related to Donze’s inability to observe the inner structures (Donze 1966).
Genus Carinobairdia Kollmann, 1963 Type species
Carinobairdia triassica triassica Kollmann, 1963 by original designation.
Remarks
Carinobairdia triassica triassica Kollmann, 1963 and C. alpina Kollmann, 1963 emend. Kristan- Tollmann 1970 are both typical for the Rhaetian, Late Triassic, of the western Tethys and Iran as shown by the occurrences lists. Until recently, Carinobairdia was restricted to the Rhaetian of the western area of the Tethys, but the discovery of a Carnian species traced the roots of this genus to the eastern Tethys (Forel et al. 2019b).
